1. Field of the Invention
This invention relates to packaging apparatus. More particularly, this invention relates to apparatus for loading stocks of perishable food product automatically into thermoformed plastic package portions while the package portions are in a loading station of a packaging machine.
2. Description of the Prior Art
One type of thermoforming and vacuum sealing packaging machine used for packaging perishable sliced food products is illustrated in U.S. Pat. No. 3,061,984. This machine comprises an endless train of trays each having two side-by-side cup-shaped forming dies which are indexed through a series of packaging stations at which successive operations are performed. As shown in the patent, the machine thermoforms one of two webs of packaging material into cup-shaped receptacles in the trays and then indexes the trays past an open area where the product groups to be packaged are inserted by hand. At the time of product loading, the cup-shaped thermoformed package portions are still held in a nested relation in the tray where they were originally formed.
A second type of thermoforming and vacuum sealing machine that is widely used in industry for packaging this class of products is illustrated in U.S. Pat. No. 3,498,021 which differs from the type previously described by having non-indexing thermoforming dies at one position, an open area for product loading, and a second set of dies which are used for evacuation and sealing. In this latter type of machine, the thermoformed web is indexed through the machine only by chains with film clamps at the two edges of the web, and may also be supported by stationary rails extending in the direction of movement. In this type of packaging machine, it may be advantageous to add a vertically reciprocating mechanism with dies to engage and support the thermoformed cups during the loading operation. It is an object of this invention to provide superior automatic loading apparatus for both types of machines described above as well as for other types not described herein.
During the early development of vacuum packaging machines of the thermoforming type, it was common practice to use only extremely thin and flexible packaging materials, at least for those portions of packages which were thermoformed into receptacles to accept the products. Thus, under vacuum, atmospheric pressure action on the outer surfaces of all sides of such packages forced the packaging materials into intimate contact and close shape conformity with the product or product groups inside. For this reason, and because of the extreme flexibility of the materials, these packages could be thermoformed considerably oversize as compared to the products without unduly stressing the packaging materials or putting undue stresses on the seals when the packages were completed. Of course, it was also relatively easy to load stacks of thinly sliced luncheon meats and like comestables into these oversized formations. Also, there was little demand during these early years for nearly perfect package appearance, and significant stacking errors and considerable product disarray were considered acceptable.
During recent years, however, two package characteristics have emerged as highly desirable or even mandatory. The first new demand was for packages having thermoformed portions made of significantly thicker and more rigid material. These packages were capable of providing spectacularly improved appearance together with enhanced user acceptance due to easier opening characteristics, the capability of reclosability, and other factors. It was quickly discovered, however, that these advantages could be obtained only by very careful control of product size, so as to provide accurate fit in the package, and by very accurate stacking of sliced products. Thus, the loose fitting, oversized, thermoformed cups and inaccurately sized products which were common practice when using flexible packages became unacceptable. As one result, hand loading of the product became more difficult, and often required much product rearrangement and manipulation by operators. The problem could not be alleviated by use of oversized formations of semi-rigid material because such packages under vacuum still collapse completely, or virtually completely, against the products, and result in very bad package appearance, often accompanied by frequent package leakage and breakage of seals.
Meat packers had been aware for some time, even prior to the introduction of semi-rigid vacuum packaging, that bacterial contamination during the slicing and packaging operations was a major cause of shortened shelf life. This contamination is caused primarily by difficult-to-clean machinery which contacts the product, and by close proximity with and/or manual handling by human operators. Thus, it is highly desirable to provide automatic loading apparatus not involving any significant human handling procedures.